Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Equal to unity

Always more than unity

Always less than unity

2. The freezing point of sulphur dioxide is

-77.7°C

-135.8°C

-75.2°C

-56.6°C

3. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

4. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

Compressor and condenser

5. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

At critical Temperature

6. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Negative

Positive

Zero

7. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Two heat exchangers

Four heat exchangers

8. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

9. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.67

0.6

0.4

10. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

3.33

4.33

1.33

Page 2 of 4

11. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Low boiling point

Good electrical conductor

High risibility with oil

12. The capillary tube, as an expansion device, is used in

All of these

Domestic refrigerators

Room air conditioners

Water coolers

13. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

14. Most thermostatic expansion valves are set for a superheat of

15°C

20°C

10°C

5°C

15. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

Ensures the evaporator completely filled with refrigerant of the load

16. Freon group of refrigerants are

Toxic

Nontoxic and non-inflammable

Inflammable

Non-inflammable and toxic

17. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Takes place at constant pressure

Involves no change in volume

18. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

19. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Miniature sealed unit

Axial

Centrifugal

20. Which of the following cycles uses air as the refrigerant?

Stirling

Ericson

Carnot

Bell Coleman

Page 3 of 4

21. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Less

Same

22. For obtaining high COP, the pressure range of compressor should be

Optimum

Any value

High

Low

23. Critical temperature is the temperature above which

Water will evaporate

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

24. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

25. Rating of a domestic refrigerator is of the order of

0.1 ton

10 tons

5 tons

40 tons

26. The boiling point of ammonia is

-30°C

-33.3°C

-10.5°C

-77.7°C

27. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

28. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Sub-cooling or under-cooling

None of these

Normal cooling

29. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

30. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

Page 4 of 4

31. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

32. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 9

1: 1

1: 3

33. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Carnot

Rankine

Reversed Rankine

34. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

35. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

36. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

37. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

38. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Brine

Freon

Ammonia

39. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

8 bar

15 bar

30 bar

40. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

Share this Now with Friends:

VideRime

A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection